Fluid cooled and perfused tip for a catheter

ABSTRACT

The invention relates to an ablation catheter which controls the temperature and reduces the coagulation of biological fluids on a tip of a catheter, prevents the impedance rise of tissue in contact with the catheter tip, and maximizes the energy transfer to the tissue, thereby allowing an increase in the lesion size produced by the ablation. The ablation catheter includes a tip for applying electrical energy to biological tissue. Passages are positioned within the tip in a variety of manners for directing a fluid flow through the tip to the exterior surface of the tip to control the temperature and form a protective fluid layer around the tip. Monitoring structure is also positioned within the tip for measurement of the electrical potentials in a biological tissue. Ablation electrode structure is also positioned within the tip for application of ablative energy to the biological tissue. A flexible, extended embodiment electrode provides the capability to form deep, linear lesions along a portion of a heart wall during ablation for the treatment of particular arrhythmias.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of application Ser. No.08/171,213, Dec. 21, 1993, now U.S. Pat. No. 5,462,521.

FIELD OF THE INVENTION

The invention relates to a flexible, fluid perfused elongated electrodefor an ablation catheter to form linear lesions in tissue.

BACKGROUND OF THE INVENTION

The pumping action of the heart is controlled in an orderly manner byelectrical stimulation of myocardial tissue. Stimulation of this tissuein the various regions of the heart is controlled by a series ofconduction pathways contained within the myocardial tissue. The impulseto stimulate is started at the sino-atrial (SA) node and is transmittedthrough the atria. The signals arrive at the atrio-ventricular (AV) nodewhich is at the junction of the atria and ventricles. The sisal passesthrough the AV node into the bundle of HIS, through the Purkinje fibersystem and finally activates the ventricular muscle. At the completionof ventricular stimulation, heart tissue rests to allow the cells torecover for the next stimulation. The stimulation is at the cellularlevel, and is a changing of the polarity of the cells from positive tonegative.

Cardiac arrhythmias arise when the pattern of the heartbeat is changedby abnormal impulse initiation or conduction in the myocardial tissue.The term tachycardia is used to describe an excessively rapid heartbeatresulting from repetitive stimulation of the heart muscle. Suchdisturbances often arise from additional conduction pathways which arepresent within the heart either from a congenital developmentalabnormality or an acquired abnormality which changes the structure ofthe cardiac tissue, such as a myocardial infarction.

One of the ways to treat such disturbances is to identify the conductivepathways and to sever part of this pathway by destroying these cellswhich make up a portion of the pathway. Traditionally, this has beendone by either cutting the pathway surgically, freezing the tissue, thusdestroying the cellular membranes, or by heating the cells, thusdenaturing the cellular proteins. The resulting destruction of the cellseliminates their electrical conductivity, thus destroying, or ablating,a certain portion of the pathway. By eliminating a portion of thepathway, the pathway no longer conducts and the tachycardia ceases.

One of the most common ways to destroy tissue by heating has been theuse of either electromagnetic energy or light. Typically, sources suchas radiofrequency (RF), microwave, ultrasound, and laser energy havebeen used. With radiofrequency energy, a catheter with a conductiveinner core and a metallic tip are placed in contact with the myocardiumand a circuit is completed with a patch placed on the patient's bodybehind the heart. The catheter is coupled to a radiofrequency generatorsuch that application of electrical energy creates localized heating inthe tissue adjacent to the distal (emitting) electrode.

Due of the nature of radiofrequency energy, both the metallic tip andthe tissue are heated simultaneously. The peak tissue temperaturesduring catheter delivered application of RF energy to myocardium occurclose to the endocardial surface, such that the lesion size produced isapproximately limited by the thermodynamics of radial heat spread fromthe tip. The amount of heating which occurs is dependent on the area ofcontact between the electrode and the tissue and the impedance betweenthe electrode and the tissue. The higher the impedance, the lower theamount of energy transferred into the tissue.

Traditional electrode configurations have a small cylindrical metal tipelectrode with one or more thin ring electrodes near the tip either toaid with ablation or to measure the impedance in nearby heart tissue.The size of the electrodes is limited because the catheter must remainflexible enough for the distal end of the catheter to be passed throughthe cardiovascular system into the heart. Solid metal electrodes limitthe flexibility of the catheter. These electrodes form a circular lesionat the point of contact on the surface of the heart tissue. The crosssection of the lesion within the heart tissue is ellipsoidal in shape.These lesions are most effective in the treatment of accessory pathways,AV node re-entrant tachycardias and some forms of idiopathic ventriculartachycardia.

However, the treatment of a broader range of arrhythmias, such as atrialfibrillation and atrial flutter, may require linear lesions. Anappropriate linear lesion would form a line on the surface of the heartand penetrate the full thickness of the heart wall. With traditional tipelectrodes described above, the only way to form such a linear lesionwould be to move the catheter during ablation to create a contiguousline from the discrete circular lesions. While this is theoreticallypossible, it is not practical to form such a line from the circularlesions because there are no visual markers that would allow thepositioning of one lesion with respect to another lesion. Generally, thelesions are not visible under fluoroscopy.

One of the major problems with radiofrequency energy is the coagulationof blood onto the tip of the catheter, creating a higher impedance orresistance to passage of electrical energy into the tissue. As theimpedance increases, more energy is passed through the portion of thetip without coagulation, creating even higher local temperatures andfurther increasing coagulum formation and the impedance. Eventually,enough blood is coagulated on the tip so that no energy passes into thetissue. The catheter must then be removed from the vascular system, thetip area cleaned and the catheter repositioned within the heart at thedesired location. This process is not only time consuming, but it isalso difficult to return with precision to the previous ablation sitebecause of the reduced electrical activity in the regions which havebeen previously ablated. Use of temperature sensors in the tip tomodulate the power input to keep the electrode below the coagulationtemperature of blood have been used. These systems inherently limit theamount of power which can be applied. Others have used closed loopcooling systems to introduce water into the tip, but these systems arelarger than necessary because the coolant must be removed from thecatheter.

In some research, an increase of impedance was noted in radiofrequency(RF) ablation at power levels above 7 watts (W) due to the formation ofa thin insulating layer of blood degradation products on the electrodesurface. Wittkampf, F. H. et al., Radiofrequency Ablation with a CooledPorous Electrode Catheter, Abstract, JACC, Vol. 11, No. 2, Page 17A(1988). Wittkampf utilized an open lumen system at the distal electrodewhich had several holes perpendicular to the central lumen which couldbe cooled by saline. Use of the saline kept the temperature of theelectrode at a temperature low enough so that the blood products wouldnot coagulate onto the tip of the electrode.

Impedance rise associated with coagulum formation during RF catheterablation was also noticed by Huang et al., Increase in the Lesion Sizeand Decrease in the Impedance Rise With a Saline Infusion ElectrodeCatheter for Radiofrequency Catheter Ablation, Abstract, Circulation,Vol. 80, No. 4, page II-324 (1989). A quadropolar saline infusionintraluminal electrode catheter was used to deliver RF energy atdifferent levels.

The drawbacks of the existing catheter electrodes are that they do notminimize the contact of biological material with the tip of the catheteralong with the cooling of the tissue in the vicinity of the tip. Whilecooling will help to reduce coagulation of blood and tissue onto thecatheter, the continued contact of the biological material with the tipwill result in further coagulation on the tip. This results in anincreased electrical resistance and a further increase in local heatingnear the tip. Another difficulty with existing catheter electrodes isthat the lesions are limited in size and shape. It is only with greatdifficulty that such electrodes can be used to form appropriate lesionsfor many cardiac arrhythmias.

SUMMARY OF THE INVENTION

The invention relates to a catheter tip for cardiac signal measurementand monitoring, including a tip structure which is positioned at the endof the catheter. Path means are formed within the tip structure fordirecting a fluid from the interior of the tip structure to portions ofthe tip structure exterior surface, thereby providing a fluid protectivelayer surrounding the tip structure. Monitoring means are also includedwithin the catheter tip structure for measurement of electricalpotentials in a biological tissue.

The invention also relates to an ablation catheter which reduces thecoagulation of biological fluids on a tip of a catheter, regulates theimpedance rise of tissue in contact with the catheter tip, and maximizesthe potential energy transfer to the tissue, producing a larger sizelesion. The ablation catheter includes a catheter body. The ablationcatheter also includes a tip for monitoring electrical potentials, andapplying electrical energy to a biological tissue. A fluid source ispositioned at one end of the catheter for supplying a fluid flow throughthe catheter to the tip means. Passages are formed within the tip fordirecting the fluid flow through the tip means to the exterior surfaceof the tip means to form a protective fluid layer around the tip.Monitoring means are also positioned within the tip structure formeasurement of the electrical potentials in a biological tissue.Ablation means are also positioned within the tip means for applicationof ablative energy to the biological tissue.

The invention also relates to an extended ablation catheter electrodethat can produce a linear shaped lesion without moving the catheter froman initial position. The elongated electrode is preferably made from afine metal mesh in electrical contact with the catheter handle.Construction of the extended electrode from the metal mesh allows theextended electrode to be sufficiently flexible that the extendedelectrode can be positioned within the heart. The inner surface of themesh is in fluid communication with path means that directs fluid fromthe interior of the catheter through the mesh to form a protective fluidlayer over the outer surface of the extended electrode.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of an ablation catheter and tip.

FIG. 2 is a fragmentary enlarged section view of the catheter tip havinga bulbous configuration.

FIG. 3 is a fragmentary enlarged section view of the catheter tip havinga spherical configuration.

FIG. 4 is a fragmentary enlarged section view of a catheter tip havingan extended rectangular shape.

FIG. 5 is a fragmentary enlarged section view of a catheter tip having arectangular shape showing the electrical conduit.

FIG. 6 is a fragmentary enlarged section view of a solid catheter tiphaving a multiplicity of discrete fluid flow passages.

FIG. 7 is a fragmentary enlarged section view of a solid catheter tiphaving a passage extending the length of the catheter tip.

FIG. 8 is a cross section view of the catheter tip showing axialchannels extending the length of the catheter tip.

FIG. 9 is a cross section view of the catheter tip showing amultiplicity of radially directed channels encircling the catheter tip.

FIG. 10 is a fragmentary enlarged section view of a catheter tip made ofa ceramic insulating material having monitoring members.

FIG. 11 is a fragmentary enlarged section view of a catheter having ringelectrodes which have path means.

FIG. 12 is a fragmentary enlarged section view of an alternativeembodiment of a catheter having a large central lumen and a smallerlumen.

FIG. 13 is a cross section view taken along line 13--13 of FIG. 12.

FIG. 14 is an enlarged fragmentary sectional view of a portion of thecatheter tip and ring electrodes shown in FIGS. 2-5, 10, and 11.

FIG. 15 is an enlarged fragmentary side perspective view of a cathetertip with an elongated flexible electrode, a tip electrode and severalring electrodes.

FIG. 16 is a fragmentary enlarged section view of a catheter tip with anextended flexible electrode, a tip electrode and several ringelectrodes.

These figures, which are idealized, are not to scale and are intended tobe merely illustrative and non-limiting.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to a catheter having a fluid perfused or insulatedtip. Fluid passes through the tip structure, forming a fluid protectivelayer around the exterior surface of the tip structure. The fluid whichpermeates and surrounds the tip structure minimizes the amount of thebiological material which comes in contact with the catheter tipstructure, as well as cools the tip structure. The cooling fluidprevents a rise in the resistance (impedance) of the tissue to energytransfer from an ablation energy source, and maximizes the potentialenergy transfer to the tissue in communication with the catheter tip. Asa result, a larger lesion size in the tissue is produced.

Referring to FIG. 1, a side elevational view of catheter 20 is shownhaving catheter body 22, a handle 24, and a tip structure 26. Catheterbody 22 may be of varying lengths, the length being determined by theapplication for catheter 20. Catheter body 22 is preferably made of aflexible, durable material, including, for example, thermoplastics suchas nylon, in which a braiding is embedded. Preferably, catheter body 22includes a large central lumen 28, such as a three French (F) lumen in afour F to twelve F, preferably eight F catheter 20. Catheter body 22 maycontain a plurality of ring electrodes 30 which surround the exteriorsurface of catheter body 22 at selected distances from the distal end 32proximate tip structure 26.

As shown in FIG. 1, handle 24 is positioned on the proximal end 34 ofcatheter body 22. Handle 24 may contain multiple ports, such as ports36, 38. Port 36 may be utilized, in this embodiment, for electricalconnections between electrophysiological monitoring equipment andelectrical potential sites of the tissue. Electrical connection means40, exiting through port 36, is positioned between and connects tipstructure 26 and the electrophysiological monitoring equipment. Port 36is in communication with central lumen 28 of catheter body 22 and mayalso be used for the introduction and passage of devices 42 throughcatheter 20. Port 38, in this embodiment, is connected to a fluid sourceand is also in fluid communication with central lumen 28 of catheter 20.Port 38 may be used for the entry of a fluid into catheter 20.Additional ports may be included on handle 24 which are in communicationwith central lumen 28. Port 36 may, for example, contain electricalconnection means 40, and an additional port may contain device 42.

Referring to FIG. 1, tip structure 26 is located at the distal end 32 ofcatheter body 22. Tip structure 26 may range from four (4) to twelve(12) French catheter tips. Tip structure 26 includes at least oneattachable electrode useful for monitoring electrical potentials of thetissue, measuring cardiac signals, and mapping to locate the tissue tobe ablated. In addition, the tip structure may include monitoring meansfor measuring, monitoring, and adjusting the rate of fluid flow throughtip 26 relative to biological parameters, such as tip and tissuetemperature.

As shown in FIGS. 2-5, the overall shape of tip structure 26 may have avariety of configurations. The various configurations may be machinedinto the material comprising tip structure 26. Preferably, the shape oftip structure 26 permits catheter 20 to proceed readily through the veinor artery into which catheter 20 may be inserted. The shape of tipstructure 26 is determined by the application for which catheter 20 isdesigned. For example, FIG. 2 is a fragmentary enlarged section view oftip structure 26 having wall portions 27 which extend beyond thediameter D of catheter portions proximal to the tip. For example, abulbous or dumbbell configuration, as shown in FIG. 2, may be useful insituations requiring access to pathway ablations which lie on top of avalve or other relatively inaccessible site. FIG. 3 illustrates afragmentary enlarged section view of tip structure 26 which has aspherical or rounded configuration which may be advantageous, forexample, in situations involving cardiac pathways underneath a valve.FIG. 4 and FIG. 5 illustrate fragmentary enlarged section views of tipstructure 26 which vary in the length of tip structure 26. Tip structure26 shown in FIG. 4 may be useful in applications which lie along themyocardial wall, and tip structure 26 illustrated in FIG. 5 may beparticularly advantageous for uses such as electrophysiological mapping.

Tip structure 26 may comprise a variety of materials. Preferably, thematerial used for tip structure 26 in the different embodiments includesa plurality of apertures or path means which are either randomly ordiscretely formed in or spaced throughout tip structure 26. The diameterof the apertures or path means is substantially smaller than the overalldiameter of tip structure 26. The diameter dimensions of the path meansin the different embodiments discussed below may vary, and may includemicroporous structures.

As illustrated in FIGS. 2-5, tip structure 26 is preferably made of asintered metal which contains a plurality of randomly formedthrough-passages or path means 48 in tip structure 26. Generally, tocreate the sintered metal for tip structure 26, spherical particles,such as finely pulverized metal powders, are mixed with alloyingelements. This blend is subjected to pressure under high temperatureconditions in a controlled reducing atmosphere to a temperature near themelting point of the base metal to sinter the blend. During sintering(heating), metallurgical bonds are formed between the particles withinthe blend at the point of contact. The interstitial spaces between thepoints of contact are preserved and provide path means for fluid flow.

Paths means 48 in tip structure 26 comprise interstitial spaces formingstructures which are randomly positioned, are of varying sizes, and areinterconnected in a random manner with other interstitial spaces in tipstructure 26 to provide fluid communication between central lumen 28 ofcatheter 20 and the exterior surface 50 of tip structure 26. Path means48 are generally five to twenty microns in diameter, although this mayvary. The metal material utilized for tip structure 26 should conductheat well, have the ability to monitor electrical potentials from atissue, and be economical to fabricate, such as stainless steel orplatinum.

Alternatively, as shown in FIG. 6, tip structure 26 may comprise a solidmetal material. FIG. 6 is a fragmentary enlarged section view ofcatheter body 22 connected to tip structure 26. Tip structure 26 in thisembodiment comprises a solid metal, such as stainless steel or platinum,having a multiplicity of specifically formed apertures or path means 52within tip structure 26 which provide fluid communication betweencentral lumen 28 of catheter 20 and the exterior surface 50 of tipstructure 26 for the passage of a fluid. The configuration of path means52 is designed to provide a continuous layer of fluid over the exteriorsurface 50 of tip structure 26. Preferably, the apertures of path means52 have a diameter less than five hundred microns, although this mayvary. The metal material utilized for tip structure 26 shown in FIG. 6should conduct heat, as well as have the ability to monitor electricalpotentials from a tissue.

FIG. 7 is a fragmentary enlarged section view illustrating catheter body22 attached to tip structure 26. Tip structure 26, in this embodiment,is preferably made of a solid metal material which conducts heat well,and has the ability to monitor and measure electrical potentials of atissue, such as stainless steel or platinum. Alternatively, tipstructure 26 may comprise a dense ceramic material. As shown in FIG. 7,a single orifice, channel or through path means 54 is formed through thelength L of tip structure 26. Path means 54 is in fluid communicationwith central lumen 28 of catheter 20. Preferably, the aperture of pathmeans 54 has a diameter less than five hundred microns, although thismay vary.

FIGS. 8 and 9 illustrate alternative cross section embodiments of tipstructure 26. FIG. 8 illustrates tip structure 26 having a plurality ofgrooves or directional channels 56 which extend in an axial directionalong the length L of tip structure 26. Interconnecting channels mayextend radially between channels 56 to aid in the fluid distributionover tip structure 26. FIG. 9 illustrates a plurality of annular groovesor directional channels 58 which encircle tip structure 26 in a radialmanner. As shown in FIG. 9, channels 60 extend between path means 54 andchannels 58 to direct the fluid flow through central lumen 28 and pathmeans 54 to the exterior surface 50 of tip structure 26. In theseembodiments, channels 56, 58 are designed to communicate with path means54 to provide a continuous, evenly distributed fluid protective layerover substantially the entire exterior surface 50 of metallic tipstructure 26.

Referring to FIG. 10, an alternative embodiment of tip structure 26 isshown. FIG. 10 is a fragmentary enlarged section view of catheter body22 attached to tip structure 26. Tip structure 26, in this embodiment,preferably comprises a ceramic insulating material which includesrandomly formed path means 61. Path means 61 are generally five totwenty microns in diameter, although this may vary. Path means 61 are influid communication with central lumen 28 of catheter 20. In addition,tip 26 includes at least one monitoring member 62 positioned throughouttip structure 26. Member(s) 62 may be of varying shapes and dimensions.Preferably, members 62 are made of a conductive material suitable formonitoring electrical activity and for application of electrical energyto a biological tissue, such as stainless steel or platinum. Tipstructure 26, in this embodiment, may contain axial or radialdirectional channels on exterior surface 50 of tip structure 26.

As shown in FIGS. 1 and 11, ring electrodes 30 may be attached tocatheter body 122. Ring electrodes 30 are connected to the monitoringequipment by electrical connection means 64 through port 36 in handle24. Electrical connection means 64 are attached to ring electrodes 30,by, for example, soldering or other suitable mechanical means. Ringelectrodes 30 may be made of a material which has path means similar topath means 48, 52, 60 as described above with reference to tip structure26 in FIGS. 2-5 and 10, and is preferably a sintered metal material. Aplurality of ring electrodes 30 may be positioned at distal end 32 ofcatheter 20. Ring electrodes 30 may be used for electrophysiologicalmonitoring and mapping, as well as for ablation. Fluid passes fromcentral lumen 28 through path means in ring electrodes 30 to form afluid protective layer around the exterior surface 66 of ring electrodes30. In a more flexible embodiment, ring electrodes 30 may be separatedby flexible plastic material forming portions of catheter body 22. Theelectrodes may be spaced at various distances, but in a flexiblearrangement may be about 1 mm to 2 mm apart.

FIG. 12 and FIG. 13 illustrate another embodiment of catheter 20. Acentral lumen 74 extends the length of catheter 20. Distal end 76 ofcatheter 20 may include a smaller diameter lumen 78 relative to lumen 74positioned substantially parallel and adjacent to central lumen 74.Lumen 74 permits the introduction of a device, such as described aboveregarding device 42, through the center of catheter 20, as well as thepassage of the fluid. Lumen 78 may be connected to port 38, and may alsobe used to direct the fluid to tip structure 26, such that the fluidpasses through path means 48, 52, 54, 61 in tip structure 26, asdiscussed above in relation to FIGS. 2-10. Non-permeable layer 82, suchas a plastic liner layer, may be positioned between lumen 74 and lumen78 to ensure that the fluid in lumen 78 is directed through passages orpath means 48, 52, 54, 61 in tip structure 26 to the exterior surface 50of tip structure 26. Ring electrodes may also be used in this embodimentto direct fluid to the exterior surface of tip structure 26 and catheter20 to form the continuous and evenly distributed fluid protective layer83 over substantially the entire exterior surface of the tip structure.

FIG. 14 illustrates an enlarged fragmentary section view of a portion ofcatheter tip structure 26 and/or ring electrodes 30 shown in FIGS. 2-5,10, and 11. Substantially spherical particles 84, preferablybiologically compatible metal particles, are positioned and arranged soas to form and create numerous interconnected, omnidirectional, tortuouspath means 48, 52, and 61 (only 48 shown) through tip structure 26.Fluid flows through these tortuous path means 48, 52, 61 in the variedtip structure configurations to the exterior surface 50 of tip structure26 or exterior surface 66 of ring electrodes 30 to uniformly and evenlydistribute the fluid around tip structure 26. Substantially all pathmeans 48, 52, 61 at surface 50 of tip structure 26 or surface 66 of ringelectrodes 30 are in fluid communication with central lumen 28.

A flexible embodiment specifically designed to produce linear lesions isshown schematically in FIGS. 15 and 16. The elongated electrode 90 ispreferably constructed from a porous or microporous mesh 91 woven fromsmall diameter metallic threads or merely configured with an appearanceof a fine weave. The porous mesh can also be constructed from a seriesof small porous metal rings closely spaced to each other. Preferably,the microporous mesh 91 covers an entire circumference near the distalend 32 of the ablation catheter. End portions of the mesh 91 aresecurely connected to the shaft through mechanical clamps, connectors oradhesive bonds 92.

The elongated electrode 90 is electrically connected to the handle 24,shown in FIG. 1, through electrical connection means 64 preferablycomprising at least one conducting wire attached to the electricalinterface connection 40 at handle 24. For ablation, appropriateelectrical current is supplied to elongated electrode 90 throughelectrical connection means 64. The electrical current can be directcurrent or alternating current, and preferably is a radiofrequencysignal. A flexible, extended embodiment electrode provides thecapability to form deep, linear lesions along a portion of a heart wallduring ablation for the treatment of particular arrhythmias. The fluidinsulating/protecting character of the invention is more important asthe electrode length increases due to the corresponding increase inpossible localized uneven heating along the length of the electrode.Such uneven heating leads to the formation of hot spots which result inbiological tissue coagulation. However, creation of this continuousfluid protective layer reduces the possibility of areas of coagulationby maintaining a more even temperature and, when using conductivesaline, creation of a conductive gap-filler material (the saline) toprovide more uniform electrical distribution of energy.

The inside surface 94 of the elongated electrode 90 is exposed to thecentral lumen 28 via a plurality of macroscopic holes 96. Holes 96 arepreferably sized between about 0.1 millimeters (mm) to about 3 mm, andpreferably about 0.2 mm to about 1.0 mm. Fluid flows from the proximalend 34 of the catheter down a fluid interface in the central lumen 28 tomacroscopic holes 96. The pressure of the fluid within the central lumen28 forces water to disperse in the annular space 98 between the shaft ofthe catheter and the fine weave forming the mesh 91. The porosity of themesh 91 is selected such that the resistance to the flow of fluidthrough the mesh 91 is significantly larger than the flow resistance atinterconnecting holes 96. This selection of porosity of the mesh 91ensures that there is an essentially even flow of fluid over the outersurface 100 of the elongated electrode 90.

Generally, the length L₁ of elongated electrode 90 is significantlylarger than the length L₂ of the ring electrodes 30. The length ofelongated electrode 90 is selected to produce the size of the linearlesion appropriate for the treatment of the patient. This length willpreferably range from about 5 mm to about 5 centimeters (cm). Thislength will often more preferably range from about 0.5 cm to about 1.5cm.

A ring electrode 30 could not be constructed with a width contemplatedfor the elongated electrode 90 because the ring electrode 30 would betoo rigid. The elongated electrode 90 is flexible similar to or evenmore than the catheter body 22. This flexibility allows the elongatedelectrode 90 to have the appropriate width without limiting thecapability of passing the distal end 32 of the catheter convenientlythrough the cardiovascular system into the heart.

The fluid introduced through ports 38, macroscopic holes 96 or otherorifices, of catheter 20 is preferably a biologically compatible fluid,and may be in a gaseous or liquid state. For example, the fluid maycomprise carbon dioxide, nitrogen, helium, water, and/or saline. Fluidenters through, for example, port 38 and is passed though central lumen28 of catheter body 22. The fluid perfuses tip structure 26 and/or ringelectrodes 30 through the path means in tip structure 26 and/or ringelectrodes 30, and creates a fluid protective layer surrounding exteriorsurfaces of tip structure 26 or exterior surfaces of electrodes 30, 90thereby minimizing contact of tip structure 26 or electrodes 30, 90 withbiological material, such as blood.

The rate of fluid flow through central lumen 28 of catheter 20 may varyand range from 0.1 ml/min. to 40 ml/min. Fluid flow through catheter 20may be adjusted by a fluid infusion pump, if the fluid is liquid, or bypressure, if the fluid is a gas. The fluid flow is regulated by theinfusion pump for the liquid fluid, or by a needle valve if a gas, so asto maintain an optimal disbursing flow over the tip structure 26 and/orelectrodes 30, 90 and maintain a desired tip temperature. Preferably,the protective layer of fluid covers all or substantially all of thesurface area of tip structure 26 and is between about 0.001 mm and 1 mm,and more preferably, about 0.01 mm. in thickness, although this may varydepending on the application, and may vary in thickness during a givenprocedure.

Temperature sensing means 47 (for example as shown in FIGS. 3 and 4) maybe incorporated into tip structure 26 for sensing and measuring thetemperature of tip structure 26 and for sensing and measuring thetemperature of the biological tissue in contact with tip structure 26.Temperature sensing means 47 may be incorporated in any of the tipstructure embodiments shown in FIGS. 2-10, 15-16. The temperaturesensing means generally comprises at least one temperature sensor, suchas a thermocouple or thermistor. In addition, temperature sensing means47 may be utilized as a feedback system to adjust the flow rate of thebiologically compatible fluid to maintain the temperature of the tipstructure at a particular temperature within a designated range oftemperatures, such as 40° C. to 95° C. Also, temperature sensing means47 may be used as a feedback system to adjust the flow rate of thebiologically compatible fluid so as to maintain the temperature of thebiological tissue in contact with tip structure 26 at a particulartemperature within a designated range of temperatures, such as 40° C. to95° C. The temperature of the tissue or tip structure 26 is controlledby the temperature of the fluid, the distribution of the fluid relativeto internal and external surfaces to the tip structure, the energyapplied to the catheter, and the fluid flow rate.

Catheter 20 may include ablation means within tip structure 26.Preferably, the ablation means may be a wire connected to an RF energysource, although other types of electrical energy, including microwaveand direct current, or ultrasound may be utilized. Alternatively, theablation means may include optical fibers for delivery of laser energy.The ablation means may be connected to an energy source through port 36,or an additional port.

As shown in FIG. 1, device 42 may be passed through central lumen 28 ofcatheter 20. Device 42 may include, for example, a guidewire for ease ofentry of catheter 20 into the heart or vascular system; a diagnosticdevice, such as an optical pressure sensor; a suction catheter forbiopsy of biological material near the distal tip; an endoscope fordirect viewing of the biological material in the vicinity of the distaltip of the catheter; or other devices.

In one example of operation, catheter body 22 of catheter 20 ispreferably percutaneously inserted into the body. The catheter ispositioned so that it lies against cardiac tissue such that the flexibleporous elongated electrode 90 makes intact along its length with thetissue area that is to be ablated. Along the line of contact, energywill flow from the conductive source to the electrode and into thecardiac tissue. Simultaneous fluid flow is maintained around theelectrode creating a buffer between the tissue and the electrode. Tipstructure 26, as an electrode, may also be utilized to measureelectrical potentials of the tissue and provide information regardingcardiac signal measurement. Electrical connection means 40 extends fromtip structure 26, through port 36, and is connected to monitoringequipment. Tip structure 26 may be utilized to map, monitor, and measurethe cardiac signals and electrical potentials of the tissue, and locatearrhthymogenic sites.

A biologically compatible fluid is introduced through port 38. The fluidpasses through a central lumen of catheter body 22 and is directed totip structure 26. The fluid passes through tip structure 26 and/or ringelectrodes 30 and/or elongated electrode 90 through path means 48, 52,54, 61 or holes 96 in a manner determined by the embodiment of distalend 32 used. The fluid perfuses tip structure 26 and forms a fluidprotective layer around exterior surface 50 of tip structure 26 and/orexterior surface 66 of ring electrodes 30 and/or the exterior surface ofthe elongated electrode 90. The fluid layer formed around catheter tipstructure 26 and/or ring electrodes 30 and/or elongated electrode 90maintains biological materials, such as blood, at a distance fromcatheter tip structure 26, thereby minimizing contact of catheter tipstructure 26 with the biological material, as well as cooling tipstructure 26 and/or elongated electrode 90. Since there is a consistent,controlled buffer layer between the biological material and catheter tipstructure 26 and/or the elongated electrode 90, the coagulation ofbiological materials is reduced and the impedance or resistance toenergy transfer of the tissue near the distal end 32 of the catheter 20is regulated and minimized during ablation.

Once the site has been located by the monitoring of theelectrophysiological signals of the tissue, the ablative energy isactivated. As a result of the fluid protective layer, the transfer ofelectrical energy to the tissue is enhanced. Increased destruction ofcardiac tissue also results from tip structure cooling since larger anddeeper lesions in the cardiac tissue are achieved than have beenpreviously possible. Use of the elongated electrode 90 allows theproduction of deep linear lesions.

The flow rate of the fluid over exterior surface 50 of tip structure 26or exterior surface 66 of ring electrodes 30 or exterior surface ofelongated electrode 90 may be accomplished in a controlled manner sothat a thin fluid film is formed around exterior surface 50, 66, 100 oftip structure 26, ring electrodes 30 and elongated electrode 90. Themaintenance of a controlled, stable, uniform fluid film alongsubstantially the entire exterior surface of tip 26, ring electrodes 30and elongated electrode 90 may be accomplished by using the variousembodiments of distal end 32 described above having a multiplicity ofpassages or path means 48, 52, 54, 61 or holes 96. Path means 48, 52,54, 61 and holes 96 permit an even, consistent distribution of minutequantities of a biologically compatible fluid over substantially theentire tip exterior surface 50 or ring electrodes exterior surface 66.

The fluid can be pumped through tip structure 26, or heat generated bythe electrical or ablation process can be used to expand the fluid andcreate a movement of fluid to the exterior surface 50, 66 of tipstructure 26 or ring electrodes 30 or elongated electrode 90. Thismovement of fluid provides a buffer or protective insulating layerbetween the exterior surface of tip structure 26 and/or ring electrode30 and/or elongated electrode 90 and the biological material, such asblood, thereby reducing the coagulation of biological materials on tipstructure 26 and/or ring electrode 30 and/or elongated electrode 90. Inaddition, the movement of fluid over and around tip structure 26 may beaided by passages or channels 56, 58 on exterior surface 50 of tipstructure 26. Cooling of tip structure 26 and/or ring electrode 30and/or elongated electrode 90 increases the lesion size produced by theablation means since the point of maximum tissue temperature is likelymoved away from tip structure 26, which allows for an altered tissueheat profile, as further described below.

Another advantage of the fluid layer buffering the surface area of tipstructure 26 and/or ring electrodes 30 and/or elongated electrode 90 isthat the fluid layer also cools the tissue adjacent tip structure 26 andelongated electrode 90 during ablation. In addition, the fluid aids inmaintaining the tissue adjacent tip structure 26 and elongated electrode90 in a cooler and potentially more conductive state, which permits moreelectricity or ablative energy to enter the tissue. As a result, largerlesions are produced because a larger voltage can be applied, producinga larger electric field without producing excessive temperatures andcoagulum formation at the tip/tissue interface. Lesions are producedwith this invention in the form of a line measuring about 1 cm to about4 cm in length and about 3 mm to about 5 mm in width whilesimultaneously maintaining the fluid protective layer. This isaccomplished without having to move the catheter and without requiringseveral ablations. Also, the greater the pressure of the fluid, the morebiological products are kept from the field of influence of, or areasurrounding, tip structure 26 and/or elongated electrode 90.

A control system may be included for controlling and regulating theelectrical potentials and temperatures in a manner that allows fordetermination of the ablation effects in the tissue. It is possible tocontrol the distribution of tissue heating by controlling thetemperature of tip structure 26 and/or elongated electrode 90 and theradiofrequency voltage, or other energy used, applied between tipstructure 26 and/or elongated electrode 90 and a reference electrode onthe surface of the body. The voltage may be set to achieve a desiredelectrical field strength, and the temperature of tip structure 26and/or elongated electrode 90 may be set to provide a desiredtemperature distribution of the tissue. The temperature distributionwill then determine the size of the lesion, i.e., the denatured proteindimensions in the myocardium.

The fluid flow rate can be regulated relative to biological parameters,such as tissue temperature, by the temperature sensing means. Forinstance, if the temperature of the tissue increases, the fluid flowrate can be increased by the regulation of the fluid infusion pump orgas needle valve. If the tissue temperature adjacent tip structure 26and/or elongated electrode 90 is not high enough, the fluid flow ratecan be decreased. This permits power to be set independently oftemperature. It is significant to note that it is normally not necessaryto remove the introduced fluid from the body.

It is also possible to generate reversible affects of ablation by use ofa cooling fluid down the central lumen 28 of catheter 20 and tipstructure 26, or by use of a low temperature controlled or elevationalheating. An area in the heart tissue is quenched with a cold or icyfluid to produce a tissue temperature of 0° C. to 30° C., or heated withelectrical energy with closed loop temperature controls as describedabove to produce tissue temperatures ranging from 40° C. to 48° C. Thosecool and warm temperatures slow the conduction of signals andtemporarily and reversibly eliminate the conduction pathways. Thistechnique may be advantageously used to see the affect on the tissuebefore the tissue is permanently affected. The heart tissue graduallyheats or cools back to normal. This technique is also advantageous sinceno catheter exchange would be required.

Various modifications and alterations of this invention will becomeapparent to those skilled in the art without departing from the scopeand spirit of this invention.

What is claimed:
 1. A catheter tip for ablation of tissue comprising:a)an elongate shaft having shaft walls defining a shaft inner lumen andshaft wall outer surfaces, the shaft having a proximal attachment endportion and a distal tip portion; b) an electrode portion comprised ofporous metal having portions mechanically connected to said shaft andelectrically connected to a conductor within said shaft, said electrodeplaced circumferentially around a portion of said shaft and having aninner surface facing toward said shaft and an outer surface facing awayfrom said shaft; and c) shaft wall structures defining fluid flowapertures extending from the shaft inner lumen to the shaft wall outersurfaces; the apertures allowing the flow of fluid from the shaft innerlumen to the porous metal electrode inner surface, and the porous metalelectrode defining fluid flow apertures suitable for the flow of saidfluid through the fluid flow apertures to create a protective layer offluid around the electrode outer surface.
 2. The catheter tip of claim 1in which the porous metal electrode comprises a sintered metal material.3. The catheter tip of claim 1 further comprising solid ring electrodesaround said shaft near said porous metal electrode, said solid ringelectrodes having an electrical connection to a conductor within saidshaft.
 4. The catheter tip of claim 1 further comprising a tip electrodeat said distal tip of said shaft, said tip electrode having anelectrical connection to a conductor within said shaft.
 5. The cathetertip of claim 1 in which the electrode portion comprises porous metalring electrodes separated by flexible plastic shaft wall segments. 6.The catheter tip of claim 1 in which the porous metal electrode portioncomprises an elongated flexible woven mesh metal structure.
 7. Thecatheter tip of claim 1 further comprising temperature sensing meansused as a feedback system for adjusting the flow rate of a fluid throughthe catheter tip.
 8. The catheter tip of claim 1 further comprisingablation means.